1. Field of the Invention
This invention relates to a communication system for transmitting and receiving data, such as audio data and image data, between a data-transmitting unit and data-receiving units connected to each other via a network.
2. Prior Art
Conventionally, there is known a communication system constituted by a data-transmitting unit, data-receiving units, and a network connecting the data-transmitting unit with the data-receiving units, wherein the data-transmitting unit generates data, such as audio data and image data, in a predetermined format (defining a data compression format, sampling frequency, etc.) and sends the generated data to the data-receiving units together with attribute information indicative of attributes of the generated data, i.e. the predetermined format, while the data-receiving units each interpret (evaluate) the received data based on the attribute information received together therewith.
The attribute information is changed, in the case of transmission of musical sound data, e.g. when an attribute of the musical sound data, such as sampling frequency, is changed between songs or tunes. In general, however, such a change in the attribute information does not occur so frequently. On the other hand, the attribute information is large in amount compared with the amount of data transmitted per unit time. Therefore, to improve the efficiency of data transmission, a method of data transmission has been conventionally employed in which the attribute information is sent only once just before transmission of data such as musical sound data, e.g. by allocating the attribute information at the head of song or tune data.
The conventional communication system employs the above method of sending attribute information on the assumption that the data-transmitting unit per se and the data-receiving units per se are not changed during data transmission, and this can cause failure of normal data transmission and reception. For example, if the data-receiving unit is changed to another data receiving unit, or a new data-receiving unit is connected to the network, i.e. the correspondence between the data-transmitting unit and the data-receiving unit is changed, before transmission of a series of data, such as data of musical pieces (musical sound data), is completed, the other or newly connected data-receiving unit does not have the attribute information immediately after the just change or the new connection, so that this unit cannot determine what format the received data has, and as a result cannot interpret the received data, whereby normal data transmission and reception cannot be instantly carried out.
One possible solution to the above problem would be to transmit attribute information, constantly or at predetermined time intervals, throughout the whole process of data transmission. However, this solution suffers from a drawback of degraded data transmission efficiency due to frequent transmission of attribute information large in amount. Further, the above technique of transmitting data at predetermined time intervals suffers from another drawback that the other or newly-connected data-receiving unit cannot obtain the attribute information instantly after the unit change or the new connection, depending on the timing thereof, and in such a case it takes a certain time period before the settings of the newly connected data-receiving unit become effective. In short, there is a problem that the data-receiving unit cannot instantly perform proper interpretation of the received data after the unit change or the new connection.
Thus, the conventional communication system suffers from incompatibility between the demand for enhanced data transmission efficiency and the demand for instant proper interpretation of the received data by data-receiving units, which is essentially difficult for the conventional communication system to overcome.